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Monte Carlo simulations of a single polyelectrolyte in solution : Activity coefficients of the simple ions and application to viscosity measurements

Ullner, Magnus LU ; Staikos, Georges and Theodorou, Doros N. (1998) In Macromolecules 31(22). p.7921-7933
Abstract

Monte Carlo simulations of linear polyelectrolytes together with explicit ions have been performed in a spherical cell model to study conformational changes and activity coefficients in relation to the isoionic dilution method used in viscosity measurements. The results show that it is possible to define an effective ionic strength that will keep the average chain conformation constant on isoionic dilution and that this ionic strength can be predicted from the activity of the counterions, as has been suggested experimentally. Activity coefficients have been calculated from the simulations and compared with theoretical estimates based on various applications of the Debye-Hückel approximation, including Manning theory and an expression... (More)

Monte Carlo simulations of linear polyelectrolytes together with explicit ions have been performed in a spherical cell model to study conformational changes and activity coefficients in relation to the isoionic dilution method used in viscosity measurements. The results show that it is possible to define an effective ionic strength that will keep the average chain conformation constant on isoionic dilution and that this ionic strength can be predicted from the activity of the counterions, as has been suggested experimentally. Activity coefficients have been calculated from the simulations and compared with theoretical estimates based on various applications of the Debye-Hückel approximation, including Manning theory and an expression for a rigid rod with discrete charges. Manning theory generally gives poor agreement with the simulations, while the rigid-rod expression, which includes an ion-ion term, is able to predict the mean activity coefficient at not too high charge densities. Assuming that the co-ions are completely inert, the rigid-rod expression also leads to a reasonable approximation for the counterion activity. The simulation results have been used as input for two theoretical expressions for the reduced viscosity. The first, which is only based on the average chain conformation, does not reproduce the qualitative features of experimental curves. Our chains, with only 80 monomers do not display large conformational changes upon dilution with salt solutions of varying ionic strength. In contrast, the second viscosity expression, which takes intermolecular electrostatic interactions into account, gives a correct qualitative behavior.

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author
publishing date
type
Contribution to journal
publication status
published
subject
in
Macromolecules
volume
31
issue
22
pages
13 pages
publisher
The American Chemical Society
external identifiers
  • scopus:0032480725
ISSN
0024-9297
DOI
10.1021/ma9804388
language
English
LU publication?
no
id
043423c0-2148-4040-acbd-c8e2355eda59
date added to LUP
2018-03-29 11:10:10
date last changed
2018-04-02 20:53:36
@article{043423c0-2148-4040-acbd-c8e2355eda59,
  abstract     = {<p>Monte Carlo simulations of linear polyelectrolytes together with explicit ions have been performed in a spherical cell model to study conformational changes and activity coefficients in relation to the isoionic dilution method used in viscosity measurements. The results show that it is possible to define an effective ionic strength that will keep the average chain conformation constant on isoionic dilution and that this ionic strength can be predicted from the activity of the counterions, as has been suggested experimentally. Activity coefficients have been calculated from the simulations and compared with theoretical estimates based on various applications of the Debye-Hückel approximation, including Manning theory and an expression for a rigid rod with discrete charges. Manning theory generally gives poor agreement with the simulations, while the rigid-rod expression, which includes an ion-ion term, is able to predict the mean activity coefficient at not too high charge densities. Assuming that the co-ions are completely inert, the rigid-rod expression also leads to a reasonable approximation for the counterion activity. The simulation results have been used as input for two theoretical expressions for the reduced viscosity. The first, which is only based on the average chain conformation, does not reproduce the qualitative features of experimental curves. Our chains, with only 80 monomers do not display large conformational changes upon dilution with salt solutions of varying ionic strength. In contrast, the second viscosity expression, which takes intermolecular electrostatic interactions into account, gives a correct qualitative behavior.</p>},
  author       = {Ullner, Magnus and Staikos, Georges and Theodorou, Doros N.},
  issn         = {0024-9297},
  language     = {eng},
  month        = {11},
  number       = {22},
  pages        = {7921--7933},
  publisher    = {The American Chemical Society},
  series       = {Macromolecules},
  title        = {Monte Carlo simulations of a single polyelectrolyte in solution : Activity coefficients of the simple ions and application to viscosity measurements},
  url          = {http://dx.doi.org/10.1021/ma9804388},
  volume       = {31},
  year         = {1998},
}